common/clock_time: wrapper for time_now() so we can override it.

diff --git a/common/Makefile b/common/Makefile
index e5d3fa69..333e3321 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -21,6 +21,7 @@ COMMON_SRC_NOGEN :=				\
 	common/channel_config.c			\
 	common/channel_id.c			\
 	common/channel_type.c			\
+	common/clock_time.c			\
 	common/close_tx.c			\
 	common/codex32.c			\
 	common/coin_mvt.c			\
diff --git a/common/clock_time.c b/common/clock_time.c
new file mode 100644
index 00000000..e3a982d7
--- /dev/null
+++ b/common/clock_time.c
@@ -0,0 +1,36 @@
+#include "config.h"
+#include <assert.h>
+#include <common/clock_time.h>
+
+static bool used = false;
+static struct timeabs dev_override;
+
+bool clock_time_overridden(void)
+{
+	return dev_override.ts.tv_sec != 0;
+}
+
+struct timeabs clock_time(void)
+{
+	used = true;
+	if (!clock_time_overridden())
+		return time_now(); /* discouraged: use clock_time so we can override */
+
+	return dev_override;
+}
+
+struct timeabs clock_time_progresses_(u64 *progress)
+{
+	if (!clock_time_overridden())
+		return clock_time();
+
+	return timeabs_add(dev_override, time_from_sec((*progress)++));
+}
+
+void dev_override_clock_time(struct timeabs now)
+{
+	assert(!used);
+
+	dev_override = now;
+	assert(clock_time_overridden());
+}
diff --git a/common/clock_time.h b/common/clock_time.h
new file mode 100644
index 00000000..a267abf4
--- /dev/null
+++ b/common/clock_time.h
@@ -0,0 +1,19 @@
+#ifndef LIGHTNING_COMMON_CLOCK_TIME_H
+#define LIGHTNING_COMMON_CLOCK_TIME_H
+#include "config.h"
+#include <ccan/short_types/short_types.h>
+#include <ccan/time/time.h>
+
+/* We use this instead of time_now, for overriding when we want reproducibility */
+struct timeabs clock_time(void);
+
+/* If you need a clock that progresses even when reproducible, use this. */
+#define clock_time_progresses() ({static u64 progress; clock_time_progresses_(&progress);})
+struct timeabs clock_time_progresses_(u64 *progress);
+
+/* dev setting to override time */
+void dev_override_clock_time(struct timeabs now);
+
+/* Did someone override time? */
+bool clock_time_overridden(void);
+#endif /* LIGHTNING_COMMON_CLOCK_TIME_H */
diff --git a/common/daemon.c b/common/daemon.c
index f7170ace..822b715a 100644
--- a/common/daemon.c
+++ b/common/daemon.c
@@ -8,6 +8,7 @@
 #include <ccan/err/err.h>
 #include <ccan/io/io.h>
 #include <ccan/tal/str/str.h>
+#include <common/clock_time.h>
 #include <common/daemon.h>
 #include <common/memleak.h>
 #include <common/randbytes.h>
@@ -202,7 +203,7 @@ void daemon_shutdown(void)
 bool daemon_developer_mode(char *argv[])
 {
 	bool developer = false, debug = false;
-	const char *entropy_override;
+	const char *entropy_override, *time_override;
 
 	for (int i = 1; argv[i]; i++) {
 		if (streq(argv[i], "--dev-debug-self"))
@@ -233,6 +234,15 @@ bool daemon_developer_mode(char *argv[])
 	if (entropy_override)
 		dev_override_randbytes(argv[0], atol(entropy_override));
 
+	/* We can also control TIME ITSELF! */
+	time_override = getenv("CLN_DEV_SET_TIME");
+	if (time_override) {
+		struct timeabs t;
+		t.ts.tv_nsec = 0;
+		t.ts.tv_sec = atol(time_override);
+		dev_override_clock_time(t);
+	}
+
 	/* This checks for any tal_steal loops, but it's not free:
 	 * only use if we're already using the fairly heavy memleak
 	 * detection. */